The present invention relates to digital broadcasts and, in particular, changing channels in a digital broadcast system.
In digital broadcasting, media programs, such as radio or television programs, are transmitted in digital format to multiple users. The digital programs can be broadcast by radio or television stations, from satellites, through cable, through a telephony network (e.g., Digital Subscriber Line (DSL)), over the Internet, or any other suitable means. More recently, for example, digital programs are broadcast over wireless or cellular networks. The broadcast programs can be received by television sets with digital receivers, desktop computers, or portable devices, such as laptop computers and handheld devices, for example, cell phones or personal digital assistants (PDAs).
The digital broadcast programs can include audio, video, data or any other media content in digital format. Typically, the broadcast programs are organized into one or more broadcast channels, where each broadcast channel represents a separate stream of media content. In some digital video broadcast systems, for example, video programs are organized into one or more video channels, where each video channel includes a separate stream of video programs. If the video programs include television programs, the video channels are traditionally referred to as television channels.
In traditional analog broadcast, data is transmitted for different broadcast channels on different carrier frequencies. Thus, data can be transmitted for multiple analog broadcast channels in parallel. In digital broadcast, however, multiple broadcast channels are often transmitted on the same one or more carrier frequencies using time division (time slicing) techniques, in which data for different broadcast channels are transmitted in different time segments or slices. Thus in digital broadcast, data is often transmitted only for one broadcast channel at a particular moment in time.
If a user switches from one broadcast channel to another, there is no perceptible delay in traditional analog broadcast, where data is broadcast for all channels in parallel. However, if a user changes channel in a digital broadcasting system that uses time division techniques, there can be a perceptible delay because a receiving device typically receives data only for one channel at any point in time. If the user switches to another broadcast channel, the receiver has to wait for the time slice in which data is broadcast for the new channel. Thus, the data often will be available for the new channel only after a noticeable delay.
The length of the delay for changing channels in a digital broadcast system depends on the implementation of the particular system. For example, if there are many channels and each requires its own respective time slice, or if relatively long time slices are used, the channel changing delay can be fairly long, for example, in the range of two to eight seconds. The delay may be exacerbated if the user is “channel surfing,” that is, repeatedly switching to new channels, for example, by repeatedly issuing a “channel up” or “channel down” command.
Furthermore, any delay associated with channel changing may be more noticeable to a user who is receiving digital broadcasts on a handheld device, such as a cell phone or PDA, because such user may have a greater expectation of “instant” access. Regardless of the reason for channel changing delay in a digital broadcast system, if a user perceives the length of the delay to be significant, the overall user experience is downgraded, which may lead to user dissatisfaction.